1. Field of the Invention
This invention relates to a method of inspecting defects on a coating film surface of a magnetic disk used as a recording medium for computers or the like. This invention particularly relates to a method of inspecting a magnetic disk surface before magnetic disks are made from a magnetic disk web.
2. Description of the Prior Art
In the course of making magnetic recording media, there has heretofore been used a method wherein a surface of a magnetic recording medium web is exposed to a light beam emitted by a light beam emission means such as a laser, receiving light reflected by the surface of the web by use of a light receiving means provided with a photomultiplier, a solar battery or the like, and detecting changes in the light amount of the reflected light, thereby to inspect defects on the web surface continuously in the web movement direction.
With the conventional technique, no problem arises in the case where a magnetic recording medium of continuous length is to be formed in the web movement direction as in the case of magnetic tapes. However, in the case where diskshaped magnetic recording media are to be made from the magnetic recording medium web as in the case of magnetic disks, some portions of the web are not utilized to form the magnetic disk products, and inspection is carried out also for such portions. Therefore, in the case where no surface defect is present at a portion utilized for forming the magnetic disk product and surface defects are present at a portion which is outside of the portion utilized for forming the magnetic disk product and which is not to be utilized for forming the magnetic disk product, it is not always possible to discriminate the portion having surface defects from the portion having no surface defect. Accordingly, the portion having surface defects plus predetermined lengths on both sides of the defective portion must be rejected for ensuring the quality of the magnetic disk product, and the product yield becomes low.